UC Berkeley

The work being presented here concentrates on characterizing flow scales of turbulent jets in the near field. Experiments were carried out with water jets and immiscible silicone oil jets of two viscosities submerged in a water tank. The jet Reynolds numbers are in the range of Re ~ 4500 - 50000 for homogeneous water jets and Re ~ 3500 - 27000 for silicone oil jets in water. To observe the turbulent/non-turbulent interface, the jet fluids are made visible by doping with fluorescent dye and excitation with directional illumination. The jet interfaces are continuous and convoluted for water jets, whereas the interfaces of the oil jets are convoluted and discontinuous with droplets and ligaments. Direct flow visualization, schlieren photography, shadowgraph photography and particle image velocimetry are employed as appropriate. Interfacial length scales are characterized using various image processing techniques for both water and oil jet runs. For the homogeneous water jet runs, streamwise internal length scales of the schlieren recording are investigated after applying temporal filters to isolate scales within the flow. When isolated based on their temporal signatures, observations of the homogeneous water jets show that the length scales of internal features increase with Reynolds number. As the Reynolds number increases, the temporal signatures of the features within the jet can be seen populating higher frequency modes. Droplet sizes for the immiscible jet runs are quantified using Hough transformation. Interface length scales decrease with Reynolds number and increase gradually with distance from the exit plane for a given Reynolds number. These scales are isotropic for the homogeneous water jets and exhibit a streamwise to cross-stream ratio of about 1.3 for the oil jets. Results indicate the average droplet size in the immiscible jets is determined by the interfacial surface tension, in relation to the Weber number.